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Comprehend Medical: a Named Entity Recognition and Relationship Extraction Web Service

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Comprehend Medical: a Named Entity Recognition and Relationship Extraction Web Service Comprehend Medical: a Named Entity Recognition and Relationship Extraction Web Service Parminder Bhatia Busra Celikkaya Mohammed Khalilia Selvan Senthivel Amazon Amazon Amazon Amazon Seattle, Washington, USA Seattle, Washington, USA Seattle, Washington, USA Seattle, Washington, USA [email protected] [email protected] [email protected] [email protected] Abstract—Comprehend Medical is a stateless and Health source NLP package based on the Unstructured Informa- Insurance Portability and Accountability Act (HIPAA) eligible tion Management Architecture (UIMA) framework [7] and Named Entity Recognition (NER) and Relationship Extraction OpenNLP [8] natural language processing toolkit. cTAKES (RE) service launched under Amazon Web Services (AWS) trained using state-of-the-art deep learning models. Contrary to uses a dictionary look-up and each mention is mapped to many existing open source tools, Comprehend Medical is scalable a Unified Medical Language System (UMLS) concept [9]. and does not require steep learning curve, dependencies, pipeline MetaMap [10] is another open-source tool aims at mapping configurations, or installations. Currently, Comprehend Medical mentions in biomedical text to UMLS concepts using dictio- performs NER in five medical categories: Anatomy, Medical nary lookup. MetaMap Lite [11] adds negation detection based Condition, Medications, Protected Health Information (PHI) and Treatment, Test and Procedure (TTP). Additionally, the service on either ConText [12] or NegEx [13]. provides relationship extraction for the detected entities as well The Clinical Language Annotation, Modeling, and Process- as contextual information such as negation and temporality in ing (CLAMP) [14] is one of the most recent clinical NLP the form of traits. Comprehend Medical provides two Application systems. CLAMP is motivated by the fact that existing clinical Programming Interfaces (API): 1) the NERe API which returns NLP systems need customization and must be tailored to all the extracted named entities, their traits and the relationships between them and 2) the PHId API which returns just the one’s task. For NER, CLAMP takes two approaches: machine protected health information contained in the text. Furthermore, learning approach using Conditional Random Field (CRF) [15] Comprehend Medical is accessible through AWS Console, Java and dictionary-based, which maps mentions to standardized and Python Software Development Kit (SDK), making it easier ontologies. CLAMP also provides assertion and negation de- for non-developers and developers to use. tection based on machine learning or rule-based NegEx. Index Terms—Neural Networks, Multi-task Learning, Natural Language Processing, Clinical NLP, Named Entity Recognition, Many of the existing NLP systems rely on ConText [12] Relationship Extraction and NegEx [13] to detect assertions such as negation. ConText extracts three contextual features for medical conditions: nega- tion, historical or hypothetical and experienced by someone I. INTRODUCTION other than the patient. ConText is an extension of NegEx, Electronic Health Records (EHR) contain a wealth of pa- which is based on regular expression. tients’ data ranging from diagnoses, problems, treatments, Most of the NLP systems discussed above perform linking medications to imaging and clinical narratives such as dis- of mentions to UMLS. They are based on pipelined compo- charge summaries and progress reports. Structured data are nents that are configurable, rely on dictionary look-up for NER important for billing, quality and outcomes. On the other and regular expressions for assertion detection. hand, narrative text is more expressive, more engaging and Recently, neural network models have been proposed to arXiv:1910.07419v1 [cs.CL] 15 Oct 2019 captures patient’s story more accurately. Narrative notes may overcome some of the limitations of rule-based techniques. also contain information about level of concern and uncertainty A feedforward and bidirectional Long Short Term Memory to others who are reviewing the note. Studies have shown that (BiLSTM) networks for generic negation scope detection was narrative notes contain more naturalistic prose, more reliable proposed in [16]. In [17] a gated recurrent units (GRUs) in identifying patients with a given disease and more under- are used to represent the clinical relations and their context, standable to healthcare providers reviewing those notes [1]– along with an attention mechanism. Given a text annotated [5]. Therefore, to have a clear perspective on patient condition, with relations, it classifies the presence and period of the narrative text should be analyzed. However, manual analysis relations. However, this approach is not end-to-end as it does of massive number of narrative text is time consuming, labor not predict the relations. Additionally, these models generally intensive and prone to errors. require large annotated corpus to achieve good performance, Many clinical Natural Language Processing (NLP) tools but clinical data is scarce. and systems were published to help us make sense of those Kernel-based approaches are also very common, especially valuable narrative text. For instance, clinical Text Analysis in the 2010 i2b2/VA task of predicting assertions. The state- and Knowledge Extraction System (cTAKES) [6] is an open- of-the-art in that challenge applied support vector machines (SVM) to assertion prediction as a separate step after entity and the relation extraction using explicit context conditioning extraction [18]. They train classifiers to predict assertions proposed in [30]. of each concept word, and a separate classifier to predict A. Named Entity Recognition Architecture the assertion of the whole entity. Augmented Bag of Words Kernel (ABoW), which generates features based on NegEx A sequence tagging problem such as NER can be formulated rules along with bag-of-words features was proposed in [19] as maximizing the conditional probability distribution over and a CRF based approach for classification of cues and scope tags y given an input sequence x, and model parameters θ. detection was proposed in [20]. These machine learning based T Y approaches often suffer in generalizability. P (yjx; θ) = P (ytjxt; y1:t−1; θ) (1) Once named entities are extracted it is important to identify t=1 the relationships between the entities. Several end-to-end mod- T is the length of the sequence, and y1:t−1 are tags for the els were proposed that jointly learn named entity recognition previous words. The architecture we use as a foundation is that and relationship extraction [21]–[23]. Generally, relationship of [31], [32]. The model consists of three main components: (i) extraction models consist of an encoder followed by rela- character encoder, (ii) word encoder, and (iii) decoder/tagger. tionship classification unit [24]–[26]. The encoder provides 1) Encoders: Given an input sequence x 2 NT whose context aware vector representations for both target entities, coordinates indicate the words in the input vocabulary, we which are then merged or concatenated before being passed first encode the character level representation for each word. to the relation classification unit, where a two layered neural (t) L×ec For each xt the corresponding sequence c 2 R of network or multi-layered perceptron classifies the pair into character embeddings is fed into an encoder, where L is the different relation types. length of a given word and ec is the size of the character Despite the existence of many clinical NLP systems, au- embedding. The character encoder employs two LSTM units −! − tomatic information extraction from narrative clinical text (t) (t) has not achieved enough traction yet [27]. As reported by which produce h1:l , and h1:l , the forward and backward hid- [27] there is a significant gap between clinical studies using den representations, respectively, where l is the last timestep in both sequences. We concatenate the last timestep of each of Electornic Health Record (EHR) data and studies using clinical −! − information extraction. Reasons for such gap can be attributed (t) (t) (t) these as the final encoded representation, hc = [hl jjhl ], to limited expertise of NLP experts in the clinical domain, lim- of xt at the character level. ited availability of clinical data sets due to the HIPAA privacy The output of the character encoder is concatenated with (t) rules and poor portability and generalizability of clinical NLP a pre-trained word embedding, mt = [hc jjembword(xt)], systems. Rule-based NLP systems require handcrafted rules, which is used as the input to the word level encoder. while machine learning-based NLP systems require annotated Using learned character embeddings alongside word em- datasets. beddings has shown to be useful for learning word level To narrow the clinical NLP adoption gap and to address morphology, as well as mitigating loss of representation for some of the limitations in existing NLP systems, we present out-of-vocabulary words. Similar to the character encoder we Comprehend Medical, a web service for clinical named entity use a BiLSTM to encode the sequence at the word level. The recognition and relationship extraction. Our contributions are word encoder does not lose resolution, meaning the output at as follows: each timestep is the concatenated output of both word LSTMs, −! − • Named entity recognition, relationship extraction and trait ht = [htjjht]. detection service encapsulated in one easy to use API. 2) Decoder and Tagger: Finally, the concatenated
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